Four fertility-related terms and concepts

For others, see the Alphabet of bioZhena at /2007/11/28/the-alphabet-of-biozhena/

Fertile phase or fertile window:

The days of the menstrual cycle, during which sexual intercourse or insemination can result in pregnancy. It includes several days leading up to and including ovulation. The exact number of the fertile days is not known. It is currently “officially” believed to be 6 days, although evidence shows that there are only 3 days of high probability of conception (while the other three days are likely due to inadequate methods of ovulation monitoring used in earlier studies). The unequivocal determination of the fertile window is a pivotal task for bioZhena. See also the previous post: /2007/12/03/fetal-sex-preselection-%e2%80%93-illustrated/

The fertile window is an empirical factor, which should be consistent with the fertilizable lifetimes of the gametes (the egg and the sperm). Those are also uncertain but currently accepted figures are up to 12 (or maybe 24) hours for the egg, and at most 3 days for the sperm. (These times must overlap, of course; they are not additive.) The historically excessive length of the officially recognized fertile phase has always been due to the absence of definitive diagnostic means. Some years ago, a reviewer of a federal grant application wrote to reject the proposal on the basis that the officially recognized required period of abstinence was about two weeks, which is impractical…

Fertility (or Fertility Status):

The female of any mammalian species, including the human female, can conceive only during a very limited period of time (a window of only a few days, arguably 3), and only if all conditions are perfect. The fertile window occurs repeatedly at intervals that are more or less regular (28 + or – 9 days or so) but their variability is substantial to the extent that planned pregnancy is a challenge. A normal healthy couple will statistically take at least 3 or 4 months to conceive, even if the concept of the fertile window is known to them. An increasing percentage of couples experience difficulties in achieving pregnancy, and reproductive specialists have found that a large percentage of women had no idea of when they could conceive.

FAM (Fertility Awareness Method):

A method of determining a woman’s fertility status through self-assessment of certain fertility signs: waking temperature (also called the basal body temperature or BBT), cervical fluid, andcervical position. While NFP users abstain, FAM users apply one of the barrier methods of contraception for vaginal intercourse during the “unsafe days” of a woman’s fertile phase. NFP stands for Natural Family Planning.

Fertilization:

The joining of an egg and sperm. More accurately, fertilization is the union of a spermatozoal nucleus, of paternal origin, with an egg nucleus, of maternal origin, to form the primary nucleus of an embryo. It is the fusion of the hereditary material of two different sex cells, or gametes, each of which carries half the number of chromosomes typical of the species.

Although sperm can swim several millimeters per second, their trip to and through the fallopian tubes is assisted or facilitated by muscular contraction of the walls of the uterus and the tubes. There is also evidence that the egg releases a chemical attractant for sperm. In any case, sperm may reach the egg within 15 minutes of ejaculation. The trip is also fraught with heavy mortality. An average human ejaculate contains several hundred million sperm but only a few hundred complete the journey. And of these, only one will succeed in entering the egg and fertilizing it. Fertilization begins with the binding of a sperm cell to the outer coating of the egg (called the zona pellucida). Enzymes, released by the acrosome at the tip of the sperm head, digest a path through the zona and enable the sperm to enter the cytoplasm of the egg.

For fascinating details, explore the developmental biology site http://zygote.swarthmore.edu/chap4.html . You will see, e.g., a photo showing the “sun in the egg”: the microtubules (stained with fluorescent antibodies to tubulin) radiating from the centrosome associated with the male pronucleus and reaching towards the female pronucleus. “This vivid image conveyed the discovery of the moment at which a new life was formed. The metaphor expressed awareness that the force of natural powers was greater than the sum of two cells.”

Then, you can read up on Homunculus: Historiographic Misunderstandings of Preformationist Terminology, an essay by Clara Pinto-Correia, abstracted from her forthcoming book, The Ovary of Eve. This essay examines the association of the term “homunculus” with the “little man” that some of the leading spermists located inside the head of the spermatozoon during the rise of theories of reproduction in the seventeenth century. You can further find out that there is “a history of speculation about sex determination that views women as incomplete males… about the notion that women are almost-men whose development or evolution is truncated… how textbooks claimed that maleness means mastery, the Y-chromosome over the X, the medulla over the cortex, androgen over estrogen…”

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One Response to “Four fertility-related terms and concepts”

  1. The Ovulona™ | bioZhena's Weblog Says:

    […] of women’s self-care. « BIOZHENA’S MISSION: A HEALTH TOOL FOR EVERY WOMAN Four fertility-related terms and concepts […]

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